The primary aim of this project is to provide psychophysical measures of accommodative amplitude over the life-span of the conscious, alert rhesus monkey to determine if age-related changes in voluntary accommodation parallel changes induced by pharmacological and electrical stimuli in the anesthetized animal. Psychophysiological methods for measuring accommodative amplitude in the rhesus monkey will be developed and standardized using a two-alternative, forced-choice discrimination task. Accommodtion will be induced by minus lenses placed in front of the eye. Voluntary accommodation will be correlated with accommodation induced by topical application of cholinomimetic drugs and by electrical stimulation of the Edinger-Westphal nuclear complex in surgically virgin animals and in animals with unilateral iridectomy. The nonbehavioral measures are available to this proposal. Age-related changes in voluntary accommodation over the entire life span will be defined and correlated with the pharmacologically and electrically-induced accomodation. Decline in visual function also will be correlated with other parameters of biological aging such as joint mobility, osteoporosis, osteoarthritis and spinal osteophytaxis. Preliminary investigations of the effects of other age-related disorders, such as cataracts, macular degeneration, and perhaps ocular hypertension and glaucoma, on visual function will be undertaken. The fundamental hypotheses of the overall project of which this research is a part include (a) that the rhesus monkey can serve as a model for study of the human accommodative mechanism and for the study of the natural history and behavioral consequences of presbyopia; (b) that through the use of non-invasive and invasive experimental approaches on this model, the etiology of presbyopia may be elucidated; and (c) that such studies may eventually lead to some means to forestall or prevent the onset of this most common ocular affliction.